A method for recording by means of an ink-jet printer, a typical method among various color recording methods, comprised generating ink droplets and depositing them onto various recording materials (such as paper, film and cloth). This method has been rapidly prevailing lately and is expected to grow remarkably in the future because of such features as less noise generation due to no contact of a recording head with a recording material and easiness in downsizing and speeding up. Conventionally, as ink for a fountain pen or a felt pen and an ink for ink-jet recording, a water-based ink dissolving a water-soluble dye in a water-based medium has been used. Therefore, in these water-soluble inks, a water-soluble organic solvent is generally added to prevent ink from clogging at a pen tip or an ink-jet nozzle. These conventional inks are required to provide a recorded image of sufficient density, not to clog at a pen tip or an ink-jet nozzle, to dry quickly on a recording material, to bleed less, to have good storage stability and, in particular, to have high solubility in water and a water-soluble organic solvent to be added to the inks. Moreover, an image formed is required to have image fastness such as water fastness, light fastness, ozone gas fastness and moisture fastness.
Ozone gas fastness, normally called ozone fastness or gas fastness in short, means durability against phenomenon that oxidizing ozone gas in the air reacts with a dye on a recording paper to incur discoloration or fading of a printed image. Although oxidizing gas having this kind of action includes NOx and SOx besides ozone gas, ozone gas is said to be a causative substance to promote the phenomenon of discoloration or fading of an ink-jet recorded image, further than these oxidizing gases. In particular, for an ink-receiving layer mounted at the surface of a paper for exclusive use for ink-jet photographic image, so as to dry the ink faster and decrease bleed on the paper of high image quality, porous materials of inorganic white pigments and the like are often used. Discoloration or fading in color caused by ozone gas occurs noticeably on such recording papers. As the phenomenon of discoloration or fading caused by oxidizing gas are characteristics of ink-jet images, improvement of ozone gas fastness is one of the most important problems.
To extend application field of a printing method using ink in the future, an ink composition to be used for ink-jet recording and a colored object thereby are strongly required to exhibit further improved water fastness, light fastness, moisture fastness and ozone gas fastness.
Among inks with various hues prepared form various dyes, a black ink is an important one used for both of mono color and full color images. So far many dye stuffs for black inks have been proposed, however, a product sufficiently satisfying market needs has not yet been provided. Many of colorants proposed are disazo ones, which have problems that they have too light hues (black with a red cast), poor color rendition, less water and/or moisture fastness, insufficient ozone gas fastness and the like. Moreover, similarly, in the case of azo metal colorant often proposed, as containing metal ions, they have problems such that considerations for human bodies and environmental safety are not exhibited enough, ozone gas fastness is not sufficient, and the like. Tetraazo colorant whose conjugated system was expanded to deepen hues leave problems such as low hues density, poor solubility in water, poor storage stability for solution and ink, insufficient ozone gas fastness and the like.
As a colorant compound for black ink used for ink-jet having improved ozone gas fastness which has been the most important assignment recently, for example, those described in Patent Literature 1 can be cited. However, the ozone gas fastness of those compounds doesn't satisfy market needs sufficiently. Furthermore, as compounds which structurally approximate to colorant compounds for black inks according to the present invention, those described in Patent Literatures 2 or 3, however, they don't satisfy market needs, particularly concerning ozone gas fastness.    Patent Literature 1: JP Laid-Open No. 183545/2003    Patent Literature 2: JP Laid-Open No. 109872/1987    Patent Literature 3: JP Laid-Open No. 201412/2003